Semiconductor devices typically have a circuit design that is repeated or duplicated within the semiconductor. Such repetition or duplication of circuitry design is provided to serve as a back up, should there be a fault or failure in one of the elements. This redundancy is included to improve the success yield rate of the manufactured semiconductor devices. Should one of the circuit elements within the semiconductor device fail, redundancy of the circuitry allows the circuit design to be changed after the processing of the semiconductor device.
One of two different ways is typically used to change the circuit design after the processing of the semiconductor devices has been completed. One of the two ways to change the circuit design is by wire bonding of the semiconductor device during assembly and packaging. The other of the two ways uses metal fuses in one of the metal interconnect layers of the semiconductor device during the processing of the semiconductor device.
In metal fuse redundancy, to deactivate or activate the desired circuitry of the semiconductor device, a selected metal fuse is deliberately damaged by the heat generated from a laser. When the heat generated by the laser reaches a certain threshold, the metal fuse is blown. Such metal fuses that are blown by a laser are typically called laser fuses. One advantage of using laser fuses is the blowing of a particular metal fuse is an automated process, which reduces the likelihood of errors. The automated process involves programming the laser device using information recovered from wafer sort, i.e. the electrical testing of the semiconductor devices after full processing of the wafers. Another advantage is that metal fuses provide increased versatility for the chip designer to provide various levels of redundancy into the semiconductor device chip design.
To obtain accurate laser fuse blowing, it is critical that the amount of diffraction be limited. Diffraction may be due to interference and phase diffraction between the laser light and the dielectric properties of layers of the semiconductor device such as oxide, dope oxide, or the like. The thickness of the inter-metal dielectrics that the laser must pass through must therefore be well controlled. The thickness of the semiconductor device surrounding the metal fuse must be within a strict range. The range depends upon the materials of the dielectrics surrounding the metal fuse of the semiconductor device. The conventional method is to have a fixed thickness of the dielectric above the metal fuse. The thickness of the dielectric depends on the laser wavelength that is used to blow the fuse and, as this differs from fabrication plant to fabrication plant, so the fixed thickness also varies between such plants. It is important is to control the final thickness of the material surrounding the fuse within a certain tolerance. There is thus a need for a method that provides specific control and accuracy of the thickness of the material of the semiconductor device surrounding the fuse of the semiconductor device.